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Chai, Guocai
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Chalapathi, D., Nordström, J., Siriki, R., Lautrup, L., Chai, G. & Kanjarla, A. K. (2024). Deformation twinning and the role of stacking fault energy during cryogenic testing of Ni-based superalloy 625. Materials Science & Engineering: A, 898, Article ID 146404.
Öppna denna publikation i ny flik eller fönster >>Deformation twinning and the role of stacking fault energy during cryogenic testing of Ni-based superalloy 625
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2024 (Engelska)Ingår i: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 898, artikel-id 146404Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Ni-based superalloys play a crucial role in various high-temperature applications, where their exceptional mechanical properties and resistance to corrosion are highly desirable. However, their response to low temperatures, especially concerning strain hardening, microstructural evolution, and deformation mechanisms, requires further scrutiny. In this study, we investigate the influence of temperature on the stacking fault energy (SFE) and its implications on deformation twinning in Alloy 625. Uniaxial tensile tests are performed at 298 K, 173 K and 77 K. The study reveals a notable increase in strain hardening at intermediate strain levels, suggesting the activation of a secondary deformation mechanism. To gain deeper insights, crystal plasticity-based simulations using the DAMASK framework are employed, complementing the experimental outcomes. Deformation twins are consistently observed at all temperatures, albeit with a small volume fraction and thickness. The critical strain for twinning decreased with decreasing temperature. Based on the numerous literature studies, experimental and computational observations, the SFE of the material is estimated to be constant over the studied temperature range.

Nyckelord
Stacking fault energy, Deformation twinning, Cryogenic testing, Crystal plasticity
Nationell ämneskategori
Metallurgi och metalliska material
Identifikatorer
urn:nbn:se:liu:diva-203479 (URN)10.1016/j.msea.2024.146404 (DOI)001219293800001 ()
Tillgänglig från: 2024-05-15 Skapad: 2024-05-15 Senast uppdaterad: 2024-05-31Bibliografiskt granskad
Chai, G., Lautrup, L. & Gustavsson, F. (2024). Extra-long creep rupture life of Alleima 3R60™ (316/316L) stainless steel. Materials at High Temperature, 41(1), 169-176
Öppna denna publikation i ny flik eller fönster >>Extra-long creep rupture life of Alleima 3R60™ (316/316L) stainless steel
2024 (Engelska)Ingår i: Materials at High Temperature, ISSN 0960-3409, E-ISSN 1878-6413, Vol. 41, nr 1, s. 169-176Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Alleima 3R60 (TM) is an AISI 316/316 L type of stainless steel. This alloy shows extra-long creep lives. At 700 degrees C with an applied stress of 45 MPa, the specimen broke first after 240 131 hours, a 140% longer creep life than the predicted. The reasons have been studied using SEM/EDS, EBSD, ECCI and TEM. Two unexpected phenomena have been observed. One is the presence of homogeneously dispersed small Mo2Fe4CrSi(Ni-0.5)f063type of precipitates in the matrix. According to the thermodynamic calculation, this phase should not form in this alloy at 700 degrees C. The other is the fine grains formed in the matrix during the creep-testing at 700 degrees C for such an extra-long time. It is believed that both small precipitates and fine grain size contribute to this extra-long creep life of the steel. With the microstructural study and thermodynamic simulation, the mechanisms to form precipitates and fine grains have been discussed.

Ort, förlag, år, upplaga, sidor
TAYLOR & FRANCIS LTD, 2024
Nyckelord
Creep; 316/316L austenitic stainless steel; fine grain size; microstructures; precipitates
Nationell ämneskategori
Metallurgi och metalliska material
Identifikatorer
urn:nbn:se:liu:diva-199546 (URN)10.1080/09603409.2023.2283989 (DOI)001108024000001 ()2-s2.0-85177448831 (Scopus ID)
Tillgänglig från: 2023-12-11 Skapad: 2023-12-11 Senast uppdaterad: 2024-06-11Bibliografiskt granskad
Ohlin, O., Siriki, R. & Chai, G. (2024). Long-term creep behaviours and structural stabilities of austenitic heat-resistant stainless steels. Materials at High Temperature, 41(1), 61-72
Öppna denna publikation i ny flik eller fönster >>Long-term creep behaviours and structural stabilities of austenitic heat-resistant stainless steels
2024 (Engelska)Ingår i: Materials at High Temperature, ISSN 0960-3409, E-ISSN 1878-6413, Vol. 41, nr 1, s. 61-72Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

For heat resistant alloys, long-term structural stability at high temperatures is a critical issue for alloy design and applications. In this paper, the long-term creep behaviours and structural stabilities of six heat resistant high Ni alloys and austenitic stainless steels have been studied. The longest creep rupture life is up to 359 283 hours. High Ni and Cr alloys show a good combination of high creep and oxidation resistances. Precipitation of nano MX particles with a very low growth rate improves long-term creep resistance at high temperatures. Long-term stable multiple nanoprecipitates of MX, Cu-rich, Laves and M23C6 phases can greatly contribute to the creep strength. Low Ni austenitic stainless steels show comparatively low oxidation and creep resistances. It was first found that at 800 & DEG;C, Cr2N could form in the low Ni steel with a long-term crept by the absorption of nitrogen from the air into the matrix.

Ort, förlag, år, upplaga, sidor
TAYLOR & FRANCIS LTD, 2024
Nyckelord
Creep; austenitic stainless steel; Ni based alloy; structural stability; microstructure
Nationell ämneskategori
Metallurgi och metalliska material
Identifikatorer
urn:nbn:se:liu:diva-198492 (URN)10.1080/09603409.2023.2263719 (DOI)001073873500001 ()
Tillgänglig från: 2023-10-16 Skapad: 2023-10-16 Senast uppdaterad: 2024-04-11Bibliografiskt granskad
Nordström, J., Dong, Z., Lautrup, L., Siriki, R., Vitos, L., Moverare, J., . . . Chai, G. (2024). Temperature study of deformation twinning behaviour in Nickel-base Superalloy 625. Materials Science & Engineering: A, Article ID 146628.
Öppna denna publikation i ny flik eller fönster >>Temperature study of deformation twinning behaviour in Nickel-base Superalloy 625
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2024 (Engelska)Ingår i: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, artikel-id 146628Artikel i tidskrift (Refereegranskat) Epub ahead of print
Abstract [en]

Deformation behaviour in the Nickel-base superalloy 625 has been studied by tensile testing at four temperatures: 295, 223, 173 and 77 K. The microstructure has been investigated using TEM, FIB-SEM, EBSD and ECCI techniques. Deformation in the alloy turns out to be a competitive course of events between at least two deformation mechanisms, namely dislocation slip and deformation twinning. Slip is the predominant deformation mechanism at higher temperatures. While at 77 K, deformation induced twinning gives an extra degree of freedom as one of the main deformation mechanisms, i.e., the material shows a twin induced plasticity, TWIP, behaviour. Ab initio calculations indicate that the influence of cryogenic/sub-zero temperatures on the stacking fault energy of this alloy can be limited and that the formation of deformation twins cannot be determined solely by the stacking fault energy. The results implies that it is the critical strain and strain hardening rate that influences the deformation twinning onset and twinning rate.

Nyckelord
Ni-base alloy, Superalloy, Deformation induced twinning, Density function theory, Stacking fault energy
Nationell ämneskategori
Metallurgi och metalliska material
Identifikatorer
urn:nbn:se:liu:diva-203601 (URN)10.1016/j.msea.2024.146628 (DOI)
Tillgänglig från: 2024-05-20 Skapad: 2024-05-20 Senast uppdaterad: 2024-05-20Bibliografiskt granskad
Chai, G., Bergström, J. & Burman, C. (2023). Crack Initiation in Bulk Matrix of Austenitic Stainless Steel during Very High Cycle Fatigue. Materials Performance and Characterization, 12(2), Article ID MPC20220094.
Öppna denna publikation i ny flik eller fönster >>Crack Initiation in Bulk Matrix of Austenitic Stainless Steel during Very High Cycle Fatigue
2023 (Engelska)Ingår i: Materials Performance and Characterization, ISSN 2379-1365, E-ISSN 2165-3992, Vol. 12, nr 2, artikel-id MPC20220094Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

In the very high cycle fatigue regime, fatigue crack initiation in high-strength steels is usually correlated to a subsurface inclusion with a fine granular area (FGA). Localized stress-strain concentration at the subsurface inclusion is a critical factor. Fatigue crack initiation with an FGA in the bulk matrix without any defect has rarely been reported. In this paper, a fundamental study on the formation of FGAs in the bulk matrix of an austenitic stainless steel has been carried out using a progressive stepwise load-increasing test with a cycle step of about 108 cycles. FGA formation in the subsurface bulk matrix has been observed. The micro structural damage in the fatigue-tested specimens has been studied using the electron channeling contrast imaging electron microscopy technique. Strain localization and grain fragmentation are the main processes for the formation of FGAs. Local plasticity exhaustion leads to crack initiation due to local stress concentrations. This method can also be used to predict the fatigue damage process, especially the damage rate in individual specimens.

Ort, förlag, år, upplaga, sidor
AMER SOC TESTING MATERIALS, 2023
Nyckelord
very high cycle fatigue; fine granular area; austenitic stainless steel; grain boundary; dislocation
Nationell ämneskategori
Annan materialteknik
Identifikatorer
urn:nbn:se:liu:diva-196680 (URN)10.1520/MPC20220094 (DOI)001023843700001 ()
Tillgänglig från: 2023-08-18 Skapad: 2023-08-18 Senast uppdaterad: 2024-04-02Bibliografiskt granskad
Chai, G., Siriki, R., Nordström, J., Dong, Z. & Vitos, L. (2023). Roles of Nitrogen on TWIP in Advanced Austenitic Stainless Steels. Steel Research International, 94(10), Article ID 2200359.
Öppna denna publikation i ny flik eller fönster >>Roles of Nitrogen on TWIP in Advanced Austenitic Stainless Steels
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2023 (Engelska)Ingår i: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, Vol. 94, nr 10, artikel-id 2200359Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

The influence of nitrogen on the mechanical properties of two high Ni containing advanced austenitic stainless steels with low stacking fault energies is investigated. The results show that increase of nitrogen content greatly increases both strength and elongation of the steel at the same time. At the cryogenic temperature, the steels show a twin induced plasticity behavior. Ab initio calculations indicate that the increase of nitrogen slightly increases the stacking fault energy and consequently the critical shear stress for twin initiation in the steel. However, addition of nitrogen significantly increases the flow stress. This leads to a smaller critical strain for twin initiation and promotes deformation twinning in the high nitrogen steel. This is confirmed by the microstructure investigation. Deformation in steels is a competitive process between slip and twinning. Dislocation slip is dominant at low strain range, but formation of stacking fault and twinning become important in the later stages of deformation. At cryogenic temperature, it is mainly deformation twinning. The influence of nitrogen addition on magnetic property and its effect on deformation twinning are also discussed. The present study increases the understanding for the development of high-performance and low-cost advanced austenitic stainless steels.

Ort, förlag, år, upplaga, sidor
Wiley-V C H Verlag GMBH, 2023
Nyckelord
austenitic stainless steels; elongation; nitrogen; strengthening; twin induced plasticity
Nationell ämneskategori
Metallurgi och metalliska material
Identifikatorer
urn:nbn:se:liu:diva-188442 (URN)10.1002/srin.202200359 (DOI)000846678800001 ()
Tillgänglig från: 2022-09-14 Skapad: 2022-09-14 Senast uppdaterad: 2024-01-10Bibliografiskt granskad
Calmunger, M., Wärner, H., Chai, G. & Segersäll, M. (2023). Thermomechanical Fatigue of Heat Resistant Austenitic Alloys. Procedia Structural Integrity, 43, 130-135
Öppna denna publikation i ny flik eller fönster >>Thermomechanical Fatigue of Heat Resistant Austenitic Alloys
2023 (Engelska)Ingår i: Procedia Structural Integrity, ISSN 2452-3216, Vol. 43, s. 130-135Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Rising global energy consumption and the increase in emissions of greenhouse gases (e.g. CO2) causing global warming, make need for more sustainable power generation. This could be accomplished by increasing the efficiency of the biomass-fired power plants, which is achieved by increasing the temperature and pressure. In addition, flexible generation of power is critical if only renewable power generation is to be achieved and this will increase the number of start-and stop cycles. Cyclic condition in a long-term high temperature environment is an operation process that such materials must withstand, in order to satisfy the needs for future power generation.

Commonly austenitic stainless steel are used for critical components of power plants. Because of future change in operating conditions, further investigations are needed to verify that the demands on safety for cyclic long-term usage is fulfilled. This work includes investigation of two commercial austenitic steels: Esshete 1250 and Sanicro 25. The materials were exposed to thermomechanical fatigue (TMF) in strain control under In-Phase and Out-of-Phase conditions and main testing temperature ranges of 100-650°C and 100-800°C respectively. Some of the specimens were pre-aged to simulate prolonged service condition. Mechanical test data were obtained and analysed in order to define the TMF performance of the investigated alloys. The differences in performance were discussed in relation to mechanical and microstructural characterization.

Ort, förlag, år, upplaga, sidor
Elsevier, 2023
Nationell ämneskategori
Metallurgi och metalliska material
Identifikatorer
urn:nbn:se:liu:diva-200462 (URN)10.1016/j.prostr.2022.12.247 (DOI)2-s2.0-85159831221 (Scopus ID)
Tillgänglig från: 2024-01-27 Skapad: 2024-01-27 Senast uppdaterad: 2024-02-01Bibliografiskt granskad
Wärner, H., Chai, G., Moverare, J. & Calmunger, M. (2022). High Temperature Fatigue of Aged Heavy Section Austenitic Stainless Steels. Materials, 15(1), Article ID 84.
Öppna denna publikation i ny flik eller fönster >>High Temperature Fatigue of Aged Heavy Section Austenitic Stainless Steels
2022 (Engelska)Ingår i: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 15, nr 1, artikel-id 84Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

This work investigates two austenitic stainless steels, Sanicro 25 which is a candidate for high temperature heavy section components of future power plants and Esshete 1250 which is used as a reference material. The alloys were subjected to out-of-phase (OP) thermomechanical fatigue (TMF) testing under strain-control in the temperature range of 100 ∘C to 650 ∘C. Both unaged and aged (650 ∘C, 3000 h) TMF specimens were tested to simulate service degradation resulting from long-term usage. The scanning electron microscopy methods electron backscatter diffraction (EBSD) and energy dispersive spectroscopy (EDS) were used to analyse and discuss active failure and deformation mechanisms. The Sanicro 25 results show that the aged specimens suffered increased plastic straining and shorter TMF-life compared to the unaged specimens. The difference in TMF-life of the two test conditions was attributed to an accelerated microstructural evolution that provided decreased the effectiveness for impeding dislocation motion. Ageing did not affect the OP-TMF life of the reference material, Esshete 1250. However, the structural stability and its resistance for cyclic deformation was greatly reduced due to coarsening and cracking of the strengthening niobium carbide precipitates. Sanicro 25 showed the higher structural stability during OP-TMF testing compare with the reference material.

Ort, förlag, år, upplaga, sidor
Basel, Switzerland: MDPI, 2022
Nyckelord
high temperature austenitic stainless steels, out-of-phase thermomechanical fatigue, crack propagation analysis, electron backscatter diffraction (EBSD), energy-dispersive X-ray spectroscopy (EDS)
Nationell ämneskategori
Materialteknik
Identifikatorer
urn:nbn:se:liu:diva-182258 (URN)10.3390/ma15010084 (DOI)000751248900001 ()35009228 (PubMedID)2-s2.0-85121749412 (Scopus ID)
Anmärkning

Funding: AB Sandvik Materials Technology in Sweden; Swedish Energy Agency through the Research Consortium of Materials Technology for Thermal Energy Processes [KME-801]

Tillgänglig från: 2022-01-11 Skapad: 2022-01-11 Senast uppdaterad: 2022-02-18Bibliografiskt granskad
Öhlin, O., Chai, G. & Siriki, R. (2022). Structural Stability of Sandvik 3R60™ After 240 131 Hours Ageing and Creep Test at 700 °C. Transactions of the Indian National Academy of Engineering, 7(2), 625-633
Öppna denna publikation i ny flik eller fönster >>Structural Stability of Sandvik 3R60™ After 240 131 Hours Ageing and Creep Test at 700 °C
2022 (Engelska)Ingår i: Transactions of the Indian National Academy of Engineering, ISSN 2662-5415, Vol. 7, nr 2, s. 625-633Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Sandvik 3R60™ is an AISI 316/316L type of stainless steel. In this paper, the structural stability of the material under long-term ageing or creep test has been studied. The material had been creep tested with a stress of 45 MPa at 700 °C. The predicted rupture time for the creep specimen was about 100,000 h; however, the specimen broke first after 240,131 h. The oxidation behavior and structural stability in both aged and creep-tested samples were studied using SEM/EDS, EBSD and ECCI techniques. Thin oxide layers near the sample surface are mainly spinel oxides and eskolaite (Cr2O3). Sigma phase, χ-phase, Eta phase, M23C6 and Cr2N have been observed in the matrix of the samples. In the crept sample, the amount of sigma phase has increased, so has Eta phase and χ-phase as well. Thermo-Calc evaluation can reasonably predict precipitation of sigma phase, Eta phase and M23C6, but not χ-phase and Cr2N phases. Creep crack initiation behavior has been studied. It is mainly noticed to start at surface oxide layer or coarse sigma particles at grain boundary or triple point. Additionally, it is also observed that the presence of a thin Cr2O3 layer between the oxide and matrix along with discontinuous sigma phase distribution at grain boundary that will reduce the risk for creep crack initiation. Further, the crack propagation behavior has also been discussed.

Ort, förlag, år, upplaga, sidor
Springer, 2022
Nyckelord
Sandvik 3R60™, structural stability, creep, precipitation, heat resistant steels, AISI 316/316L
Nationell ämneskategori
Materialteknik
Identifikatorer
urn:nbn:se:liu:diva-181431 (URN)10.1007/s41403-021-00298-9 (DOI)
Forskningsfinansiär
Linköpings universitet
Tillgänglig från: 2021-11-26 Skapad: 2021-11-26 Senast uppdaterad: 2022-11-28Bibliografiskt granskad
Mondal, R., Kumar Bonagani, S., Raut, P., Kumar, S., Sivaprasad, P. V., Chai, G., . . . Samajdar, I. (2021). Dynamic Recrystallizatin and Phase-Specific Corrosion Performance in a Super Duplex Stainless Steel. Journal of materials engineering and performance (Print), Article ID 11665.
Öppna denna publikation i ny flik eller fönster >>Dynamic Recrystallizatin and Phase-Specific Corrosion Performance in a Super Duplex Stainless Steel
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2021 (Engelska)Ingår i: Journal of materials engineering and performance (Print), ISSN 1059-9495, E-ISSN 1544-1024, artikel-id 11665Artikel i tidskrift (Refereegranskat) Epub ahead of print
Abstract [en]

Super duplex stainless steel specimens were subjected to controlled (in a deformation simulator) thermal and thermal plus deformation treatments. The objective was to relate the corrosion performance with hot (1000-1300°C) deformed microstructures. The microstructural evolutions were quantified with extensive microtextural characterization and measurements of phase-specific micro-hardness. The corrosion behavior was investigated by anodic polarization and phase-specific selective dissolution methods. Though the thermal treatment imposed an increasing degradation in corrosion performance with holding temperature, the associated deformation at that temperature brought a non-monotonic behavior. The best corrosion performance (or the lowest passivation current density) was noted in the specimen deformed at ~1100°C. This superior corrosion behavior was attributed to the grain size refinement in the austenite phase. Finally, a combination of transmission Kikuchi diffraction (TKD) plus transmission electron microscopy (TEM) clearly related the grain size refinement to discontinuous dynamic recrystallization. The overall corrosion behavior was shown to be determined by a balance between decreasing austenite fraction and dynamic recrystallization-induced grain size refinement of the austenite phase.

Ort, förlag, år, upplaga, sidor
ASM International, 2021
Nationell ämneskategori
Materialteknik
Identifikatorer
urn:nbn:se:liu:diva-180806 (URN)10.1007/s11665-021-06221-1 (DOI)000698037800001 ()2-s2.0-85115227854 (Scopus ID)
Tillgänglig från: 2021-11-02 Skapad: 2021-11-02 Senast uppdaterad: 2021-11-09Bibliografiskt granskad
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